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Tape, disk or both in a SAN environment?

I will be setting up a SAN environment in the next few months. I was warned not to combine both disk and tape on the same SAN because it causes problems and vendors are pointing at each other when the problems occur.

All of the reading I have done says this should not be a problem providing I have defined the segments correctly. Should I build two SAN environments? One for my shared disk pools and another for my tape devices used for backup? I will be using Veritas for SAN, file, disk, and backup management; and STK/Brocade* for Silo/tape/switches. (*Brocade with STK branding)

Thanks.

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You are correct in stating that putting disk and tape on the same SAN should not be a problem, provided that you are not using an arbitrated loop (FC-AL) solution for both disk and tape in the SAME loop.

It is usually wise to use a separate HBA for tape backup so that backup operations do not use all your bandwidth during production runs. You can share an adapter for both disk and tape access as long as you're in a switched environment. This allows for a cheaper implementation but backup will impact production if using the same adapter. Tape rewinds at times cause a SCSI reset to be sent on a shared loop and this may cause LIPs during disk access, which is not a good thing.

I usually provide two HBAs for resiliency to disk and a third for tape into the same SAN. You can then use zoning to zone the tape access to the tape HBA.

Chris

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This was first published in February 2002

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